Method and apparatus for assuring proper media feeding

ABSTRACT

This invention relates to an apparatus for assuring media feeding, comprising: an impression drum having a media gripper; an input feed unit located substantially adjacent to the impression drum for feeding a sheet of media; and a servo motor operatively connected to the input feed unit such that a change in operating characteristics of the servo motor is detected if the sheet of media is properly retained by the gripper.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for assuring media feeding,comprising: an impression drum having a media gripper; an input feedunit located substantially adjacent to the impression drum for feeding asheet of media; and a servo motor operatively connected to the inputfeed unit such that a change in operating characteristics of the servomotor is detected if the sheet of media is properly retained by thegripper.

2. Description of the Related Art

Prior to the present invention, as set forth in general terms above andmore specifically below, it is known, in the printing art to employsensors at the entrance between the impression drum and the intermediatetransfer drum in order to detect the media leading-edge position andtiming. While this system is capable of detecting the leading edge andtiming of the media, this solution requires additional sensors inside ofthe printing device. Also, the leading edge position and timing of themedia are detected outside of the media grippers that can result in aninadequate detection of paper stick to blanket (PSTB). Finally, thesensors of this system may send faulty alarms due to dirt and paper dustadversely affecting the sensors. Consequently, a more advantageoussystem, then, would be provided if such sensors can be avoided.

It is also known, in the printing art to employ a pressurized system todetermine if the media is located against the impression drum. In thismanner, a vacuum is applied to the impression drum. If a sheet of mediais located on the impression drum, a change in the vacuum properties isdetected. While this system is capable of detecting the presence themedia, this solution requires additional sensors inside of the printingdevice. Also, the system is not capable of detecting if the media isproperly located within grippers. Finally, the vacuum sensors of thissystem may send faulty alarms due to vacuum ports becoming inadvertentlyclogged. Therefore, a further advantageous system, then, would beprovided if such a vacuum system could be avoided.

It is apparent from the above that there exists a need in the art for amethod and apparatus for assuring proper media feeding such that theproper retention of the media within the grippers can be detectedwithout the use of sensors or other complicated systems so as to avoidpaper stick to blanket (PSTB). It is a purpose of this invention tofulfill this and other needs in the art in a manner more apparent to theskilled artisan once given the following disclosure.

SUMMARY OF THE INVENTION

Generally speaking, an embodiment of this invention fulfills these needsby providing an apparatus for assuring media feeding, comprising: animpression drum having a media gripper; an input feed unit locatedsubstantially adjacent to the impression drum for feeding a sheet ofmedia; and a servo motor operatively connected to the input feed unitsuch that a change in operating characteristics of the servo motor isdetected if the sheet of media is properly retained by the gripper.

In certain preferred embodiments, the input feed unit is a plurality ofrollers that create a nip to feed the sheet of media towards theimpression drum. Also, if a change in the torque on servo motor isdetected then it can be assumed that the sheet of media is properlyretained by the gripper. Finally, if a change in the velocity of theservo motor is detected, then it can be assumed that the media has notbeen properly retained by the grippers.

In another further preferred embodiment, a method and apparatus ispresented for assuring proper media feeding such that the properretention of the media within the grippers can be detected without theuse of sensors or other complicated systems so as to avoid paper stickto blanket (PSTB).

The preferred method and apparatus for assuring media feeding, accordingto various embodiments of the present invention, offers the followingadvantages: ease-of-use; elimination of extraneous sensors; improveddetection times; reduced printer downtime; decreased paper stick toblanket occurrences; and reduced blanket damage. In fact, in many of thepreferred embodiments, these factors of elimination of sensors, improveddetection times, reduced printer downtime, decreased paper stick toblanket occurrences, and reduced blanket damage are optimized to anextent that is considerably higher than heretofore achieved in prior,known method and apparatus for assuring media feeding.

The above and other features of the present invention, which will becomemore apparent as the description proceeds, are best understood byconsidering the following detailed description in conjunction with theaccompanying drawings, wherein like characters represent like partsthroughout the several views and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a method and apparatus forassuring proper media feeding wherein the media has reached the gripperson time, according to another embodiment of the present invention;

FIG. 2 is a schematic illustration of a method and apparatus forassuring proper media feeding wherein the media has missed the grippers,according to another embodiment of the present invention;

FIG. 3 is a graphical illustration of paper velocity at various feedstages (time (ms) versus paper velocity (mm/s)), according to the priorart;

FIG. 4 is a graphical illustration of paper velocity with servodetection at various feed stages (time (ms) versus paper velocity(mm/s)) as the media enters into the grippers properly, according toanother embodiment of the present invention; and

FIG. 5 is a graphical illustration of paper velocity with servodetection at various feed stages (time (ms) versus paper velocity(mm/s)) as the sheet of media misses the grippers, according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The paper stick to blanket (PSTB) phenomenon is one of the main reasonsfor blanket (the soft material that is wrapped around the ITM drum)damage due to its interaction with jammed media. When PSTB occurs, theprinter stops printing and the operator must then get to the blanket.The jammed media and any residual ink must be cleaned from the blanket.During this operation, the image may be fused to the blanket and thenthe operator is forced to replace the blanket. Also, in some cases, thejammed media may become bent and this bend may cause a mechanical defectin the blanket, which may also force the operator to place to blanket.It is to be kept in mind that under normal operating conditions, ittakes about 30 milliseconds between the time the grippers are closed andthe grippers reach the next drum. Clearly, media jamming is an issueand, even greater, is the concern of how to quickly determine that amedia jammed has occurred in order to avoid undue amounts of lostdowntime.

With this background in mind, apparatus 2 for assuring proper mediafeeding is illustrated in FIGS. 1 and 2. Apparatus 2 includes, in part,conventional ITM drum 4, conventional impression drum 6, conventionalgrippers 8, input feed unit 10, a sheet of the media 12, servo motor 14,and servo motor controller 16. Preferably, input feed unit 10 includes aplurality of rollers that create a nip. This nip interacts with media 12in order to feed media 12 towards impression drum 6 and grippers 8.Servo motor 14, preferably, is operatively connected to input feed unit10 and is any suitable electromechanical mechanism that supplements aprimary control operated by comparatively feeble force through servomotor controller 16. It is to be understood that controller 16 can bepart of servo motor 14 or located outside of servo motor 14.

FIGS. 1 and 2 illustrate two scenarios that can occur with respect toapparatus 2. In the first scenario, media 12 properly enters intogrippers 8, as illustrated in FIG. 1. In FIG. 1, input feed unit 10pushes the media 12 to cause the media 12 to move towards the nipbetween ITM drum 4 and impression drum 6 and at the right time, apply atension force. Media 12 properly enters into grippers 8. Grippers 8 willpull media 12 against input feed unit 10 and servo motor 14. Thispulling creates a negative pulling force (tension mode) on servo motor14. It is to be understood that the pulling force of grippers 8 shouldbe greater than the driving force of servo motor 14 on input feed unit10 so that grippers 8 are capable of pulling media 12 through input feedunit 10 but not great enough to rip or otherwise adversely affect media12 or pull media 12 out of grippers 8. At this point, servo motorcontroller 16 will detect a change at the velocity levels (or currentlevels) of servo motor 14 and will cause input feed unit 10 toaccelerate the velocity of media 12 so that it is equal to the processvelocity (the velocity of media 12 at grippers 8) in order to avoidunnecessary tension upon media 12. In this manner, the proper grippingof media 12 by grippers 8 can be quickly and easily detected.

With respect to FIG. 2, input feed unit 10 pushes the media 12 to causethe media 12 to move towards the nip between ITM drum 4 and impressiondrum 6 and at the right time, apply a tension force. In this Figure,media 12 misses grippers 8. It is to be understood that media 12 maymiss the grippers 8 for a variety of reasons. For example, there may bea delay in the conveyor (not shown) that feeds media 12 into input feedunit 10. Also, media 12 may be skewed when it reaches grippers 8. Also,there may be a malfunction in the mechanical system which controls thegripper's actuation. Finally, there may be a malfunction in input feedunit 10 which feeds media 12 into grippers 8. Due to the fact that media12 misses or otherwise does not properly engage with grippers 8, therewill be no tension force on servo motor 14 on that will resist againstgrippers 8 and pull media 12 away from grippers 8. In this manner, servomotor controller 16 will detect a decreased change in velocity level (orcurrent level) of servo motor 14 and stop media 12 from entering intothe nip between ITM drum 4 and impression drum 6. Consequently, PSTBwill be efficiently detected and prevented.

To demonstrate further proof of the concepts of the present attention,FIGS. 3-5 are presented. With respect to FIG. 3, a conventional currentinput feed unit operation is driven by a stepper motor, according to theprior art. As shown in the graph, media reaches the input feed unit,stops, and, at the right moment, the media is fed into the impressiondrum grippers. During the movement of the media, the input feed unitaccelerates and decelerates the media until the media reaches thegrippers. When the grippers close, the media velocity is equal to theprocess velocity (the velocity of the grippers). The input feed unitdrives the media at this velocity until the trailing edge of the sheetof media exits the input feed unit.

FIG. 4 is a graphical illustration showing how the media enters into thegrippers properly, according to the present invention. As shown in FIG.4, grippers 8 (FIGS. 1 and 2) will pull media 12 against servo motor 14to create a negative pulling force (tension mode) on servo motor 14. Thepulling force of grippers 8 should be greater than the force applied byinput feed unit 10 and servo motor 14 so that grippers 8 will pull media12 through input feed unit 10. Servo motor controller 16 will detect achange in velocity levels (or current levels) of servo motor 14 and willaccelerate the velocity of media 12 through input feed unit 10 so thatit is equal to the process velocity (the velocity of grippers 8) inorder to avoid unnecessary tension on media 12. In this manner, theproper retention of media 12 within grippers 8 can be efficientlydetected.

FIG. 5 is a graphical illustration showing how the media missed thegrippers, according to present invention. As shown in FIG. 5, input feedunit 10 will apply a tension force to media 12. Due to the fact thatmedia 12 misses grippers 8, there will be no tension force on media 12by grippers 8 that will pull media 12. Due to this loss of tensionforce, the velocity of media 12 will be reduced. Servo motor controller16 will detect this change in velocity of media 12 through input feedunit 10 and stop media 12 from entering into the nip between ITM drum 4and impression drum 6. In this manner, PSTB will be efficiently detectedand prevented.

The present invention can be embodied in any computer-readable mediumfor use by or in connection with an instruction-execution system,apparatus or device such as a computer/processor based system,processor-containing system or other system that can fetch theinstructions from the instruction-execution system, apparatus or device,and execute the instructions contained therein. In the context of thisdisclosure, a “computer-readable medium” can be any means that canstore, communicate, propagate or transport a program for use by or inconnection with the instruction-execution system, apparatus or device.The computer-readable medium can comprise any one of many physical mediasuch as, for example, electronic, magnetic, optical, electromagnetic,infrared, or semiconductor media. More specific examples of a suitablecomputer-readable medium would include, but are not limited to, aportable magnetic computer diskette such as floppy diskettes or harddrives, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory, or a portable compact disc. Itis to be understood that the computer-readable medium could even bepaper or another suitable medium upon which the program is printed, asthe program can be electronically captured, via, for instance, opticalscanning of the paper or other medium, then compiled, interpreted orotherwise processed in a single manner, if necessary, and then stored ina computer memory.

Those skilled in the art will understand that various embodiment of thepresent invention can be implemented in hardware, software, firmware orcombinations thereof. Separate embodiments of the present invention canbe implemented using a combination of hardware and software or firmwarethat is stored in memory and executed by a suitableinstruction-execution system. If implemented solely in hardware, as inan alternative embodiment, the present invention can be separatelyimplemented with any or a combination of technologies which are wellknown in the art (for example, discrete-logic circuits,application-specific integrated circuits (ASICs), programmable-gatearrays (PGAs), field-programmable gate arrays (FPGAs), and/or otherlater developed technologies. In preferred embodiments, the presentinvention can be implemented in a combination of software and dataexecuted and stored under the control of a computing device.

It will be well understood by one having ordinary skill in the art,after having become familiar with the teachings of the presentinvention, that software applications may be written in a number ofprogramming languages now known or later developed.

Once given the above disclosure, many other features, modifications orimprovements will become apparent to the skilled artisan. Such features,modifications or improvements are, therefore, considered to be a part ofthis invention, the scope of which is to be determined by the followingclaims.

1. An apparatus for assuring media feeding, comprising: an impression drum having a media gripper; an input feed unit located substantially adjacent to the impression drum for feeding a sheet of media; and a servo motor operatively connected to the input feed unit such that a change in operating characteristics of the servo motor is detected if the sheet of media is properly retained by the gripper.
 2. The apparatus, as in claim 1, wherein the input feed unit is further comprised of: a plurality of rollers that create a nip.
 3. The apparatus, as in claim 1, wherein the apparatus is further comprised of: a servo motor controller operatively connected to the servo motor to control operating characteristics of the servo motor.
 4. The apparatus, as in claim 1, wherein the apparatus is further comprised of: a ITM drum located substantially adjacent to the impression drum so as to create a nip between the impression drum and the ITM drum.
 5. A method for assuring media feeding, comprising: pushing a sheet of media by an input feed unit to cause the media to move towards an impression drum; determining a velocity of the input sheet unit; detecting a change in the velocity of the input feed unit; and determining if the media has been properly retained in media grippers substantially located on the impression drum.
 6. The method, as in claim 5, wherein the method is further comprised of: allowing the media to enter into the media grippers; pulling the media by the grippers such that the media will pull against the input feed unit; creating a negative pulling force on the input feed unit; detecting the change in a velocity level of the input feed unit; and accelerating the velocity of the input feed unit so that it becomes equal to a velocity of the grippers.
 7. The method, as in claim 6, wherein the pushing step is further comprised of: operating a servo motor operatively connected to the input feed unit to cause the media to move towards an impression drum.
 8. The method, as in claim 6, wherein the pulling step is further comprised of: creating a pulling force that should be greater then a driving force of the input feed unit but not great enough to adversely affect the media or pull the media out of the grippers.
 9. The method, as in claim 7, wherein the detecting step is further comprised of: operatively connecting the servo motor to the input feed unit; detecting a change in velocity level of the servo motor; and employing a servo motor controller to detect the change in the velocity of the servo motor.
 10. The method, as in claim 9, wherein the accelerating step is further comprised of: operating the servo motor in order to change the velocity of the input feed unit.
 11. The method, as in claim 5, wherein the method is further comprised of: the media does not properly engage with the grippers; creating a decreased velocity of the input feed unit; and stopping the media from moving towards the impression drum.
 12. The method, as in claim 11, wherein the step of creating a decreased velocity is further comprised of: eliminating any tension force that is applied upon the input feed unit by the media.
 13. A program storage medium readable by a computer, tangibly embodying a program of instructions executable by the computer to perform method steps for assuring media feeding, comprising: pushing a sheet of media by an input feed unit to cause the media to move towards an impression drum; determining a velocity of the input sheet unit; detecting a change in the velocity of the input feed unit; and determining if the media has been properly retained in media grippers substantially located on the impression drum.
 14. The method, as in claim 13, wherein the method is further comprised of: allowing the media to enter into the media grippers; pulling the media by the grippers such that the media will pull against the input feed unit; creating a negative pulling force on the input feed unit; detecting the change in a velocity level of the input feed unit; and accelerating the velocity of the input feed unit so that it becomes equal to a velocity of the grippers.
 15. The method, as in claim 14, wherein the pushing step is further comprised of: operating a servo motor operatively connected to the input feed unit to cause the media to move towards an impression drum.
 16. The method, as in claim 14, wherein the pulling step is further comprised of: creating a pulling force that should be greater then a driving force of the input feed unit but not great enough to adversely affect the media or pull the media out of the grippers.
 17. The method, as in claim 15, wherein the detecting step is further comprised of: operatively connecting the servo motor to the input feed unit; detecting a change in velocity level of the servo motor; and employing a servo motor controller to detect the change in the velocity of the servo motor.
 18. The method, as in claim 17, wherein the accelerating step is further comprised of: operating the servo motor in order to change the velocity of the input feed unit.
 19. The method, as in claim 13, wherein the method is further comprised of: the media does not properly engage with the grippers; creating a decreased velocity of the input feed unit; and stopping the media from moving towards the impression drum.
 20. The method, as in claim 19, wherein the step of creating a decreased velocity is further comprised of: eliminating any tension force that is applied upon the input feed unit by the media. 